On Fri, 2008-07-25 at 00:09, David Woolley (E.L) wrote: > FIR filters cannot ring in the full sense of the word. What they can do > is to generate a finite pulse of a particular frequency, but that pulse > is never longer than the filter length. Long filter lengths result in a > delay in the signal, which can become unacceptable in itself, so systems > are not designed with extremely long filters.
For signals received by the human ear, the filter length would have to be really long to be objectionable. For a symmetrical impulse response, the delay is 1/2 the filter length. For example, assuming a 10 kHz sample rate and a 1000-tap filter, the delay is only 1/20 second. To get a decent shape factor, the filter length in seconds needs to be at least a few times 1/bandwidth. Say 10/BW or so, resulting in 5/BW delay. So even with a 50 Hz bandwidth, the delay only needs to be on the order of 1/10 second. I don't think you'd ever notice that in normal on-the-air operation. Al N1AL _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
